1. Field of the Invention
This invention relates to a video disc reproducing apparatus provided with a pickup means by which the information recorded on a video disc is detected as a variation in electrostatic capacity.
2. Description of the Prior Art
Conventionally, the video disc reproducing apparatus of an electrostatic capacity detection system type rotates the video disc while contacting at the surface thereof with a pickup needle, whereby minute dust enters between the disc and the needle point. As a result, an output of reproduced signal picked up by the pickup needle point lowers, thereby creating a problem of a deteriorating signal-to-noise ratio. For preventing the deterioration of the reproduced signal caused by the sticking dust, it has been found that one effective remedy for the above is to increase pressure of the pickup needle when dust sticks to its point. Furthermore, it has been found from the recent research that the amplitude of reproduced output signal begins to lower when dust begins to stick to the needle point so that the amplitude greatly lowers as the dust accumulates, in which if the needle pressure slightly increases while dust accumulates still a little, the dust is easily removable and thereafter hard to accumulate. Also it is effective for removal of dust to control the pickup needle pressure corresponding to the amplitude of reproduced signal. However, the needle pressure, when controlled by control voltage proportional merely to the amplitude of reproduced signal, leads to a change also due to disparities in the amplitude of the reproduced signal. In other words, variations in the disc or pickup needle will cause the disparities in the reproduced signal, in which the needle pressure also will have changed. Next, explanation will be given on the above matter according to FIG. 1, in which the axis of abscissa represents the signal amplitude and the axis of ordinate the control voltage proportional thereto. Now, assuming that the signal amplitude is reproduced at 5 V and lowers by sticking dust so that the control voltage drops only by .DELTA.V, it is meant that the signal amplitude at that time lowers by 20% from 5 V to 4 V. However, for example, in a case of using a poor disc to reproduce the signal amplitude at 2 V, the output signal in turn lowers by 50% from 2 V to 1 V. In brief, since a rate of change differs with respect to the constant value of control voltage, the signal is not usable for controlling the needle pressure.